Hydrogen storage metal alloy and production thereof

ABSTRACT

A process for producing hydrogen storage metal alloys having a body-centered cubic structure-type main phase enabling the adsorption and desorption of hydrogen is provided which comprises the steps of: (1) melting a starting alloy brought to a predetermined element ratio to form a uniform heat (melting step), (2) keeping the homogenized alloy heat at a temperature within a range just below the melting point of the alloy for a predetermined time (heat treatment), and (3) rapidly cooling the alloy after the heat treatment (quenching step).

TECHNICAL FIELD

The present invention relates to a hydrogen storage metal alloy capableof repeatedly carrying out the absorption and release of hydrogen. Inparticular, the present invention relates to a BCC system hydrogenstorage metal alloy having theoretically a high capacity for hydrogenstorage. Further, the present invention especially relates to a hydrogenstorage metal alloy having a highly practicable property, including, forexample, not only quantitatively excellent hydrogen adsorption anddesorption characteristics within practical pressure ranges andtemperature ranges but also a capacity of adsorbing and desorbinghydrogen in quite great amounts per unit weight, together with arelatively inexpensive producibility, and to a process for productionthereof.

RELATED ART OF THE INVENTION

At present, there have been worried not only about acid rain due to anincreasing NOx (nitrogen oxides) but also about the global warming dueto an increasing CO₂ in association with an increase in consumption offossil fuel such as petroleum. Such environmental destruction has becomea serious problem. Therefore, our attention has been greatlyconcentrated on development and practical application of various kindsof clean energy which is friendly to the earth. Part of means fordeveloping such a new energy is a practical application of hydrogenenergy. Hydrogen is a constituent element of water inexhaustibly presenton the earth and can be not only produced using various kinds of primaryenergy but also utilized as fluid energy in place of conventionally usedpetroleum without the risk of destroying the environment because itsproduct by combustion is only water. In addition, unlike electricity, ithas excellent characteristics such as its relatively easy storage.

In recent years, therefore, investigation has been actively conductedinvolving hydrogen storage metal alloys as media for storage andtransport of hydrogen, and their practical application has beenexpected. Such hydrogen storage metal alloys are metals/alloys which canabsorb and release the hydrogen under an appropriate condition and, bythe use of such alloys, it is possible to store the hydrogen not only atlower pressure but also at higher density as compared to the case of theconventional hydrogen cylinders. In addition, the hydrogen volumedensity thereof is nearly equal to or rather more than that of liquid orsolid hydrogen.

These hydrogen storage metal alloys which have been practically useduntil now are AB₅ alloys such as LaNi₅ and AB₂ alloys such as TiMn₂, buttheir hydrogen absorbing capacity is still insufficient. In recentyears, for example, as proposed in Japanese Unexamined PatentPublication (Kokai) No. 10-110225 (JP, A, 10-110225), metals/alloys (themetal includes V, Nb, Ta, etc. and the alloy does TiCrV alloys, etc.)each having a body-centered cubic (hereinafter, referred to as “BCC”)structure have been mostly investigated because the number of hydrogenabsorbing sites in the crystal lattice is great in the BCC structure andthe hydrogen absorbing capacity is as large as H/M=ca. 2 wherein H isoccluded hydrogen and M is a constituent element for the alloy (about4.0 wt %, i.e., it is huge, in alloys of V, etc. having an atomic weightof around 50).

With regard to alloys wherein Ti and Cr are comprised, it has beenreported as follows: as suggested in JP, A, 10-110225, when for alloyscomprised of only Ti and Cr the admixture ratio of the constituentmetals is brought to such an extent that it will be conductible toabsorb and release hydrogen at a practicable temperature and pressure(i.e., the atomic ratio of Ti is set at 5<Ti (at %)<60), as alsoapparent from FIG. 2 (phase diagram for the Ti—Cr binary alloy), atemperature range for forming a BCC structure becomes very narrowbetween a melting point of the alloy and a temperature at which a Cl4crystal structure is formed. Consequently, other Cl4 crystal structurephases which are different from BCC are formed at 90 wt % or more in thealloy and it is very difficult to produce the BCC. Therefore, V isadmixed as an element highly capable of forming BCC together with bothTi and Cr in order to attain the BCC structure in a more stable fashionand at a lower temperature. As a result, the aforementioned TiCrV alloyshave been produced wherein, unless the amount of V is at least 10% ormore, it is difficult to form the BCC as their main phase even byapplication of heat-treatment whereby no good hydrogen adsorption anddesorption characteristics are obtainable.

A Ti—Cr based alloy (comprised of 5 or more elements) having theformula:Ti_((100-x-y-z))Cr_(x)A_(y)B_(z)wherein A is one member selected from V, Nb, Mo, Ta and W, B is two ormore members selected from Zr, Mn, Fe, Co, Ni and Cu, and itscrystalline structure is BCC is disclosed in Japanese Unexamined PatentPublication (Kokai) No. 7-252560 (JP, A, 7-252560) and it is pointed outtherein that the aforementioned admixture of 5 or more elements isessential for acquiring the aforementioned BCC.

However, there are still problems: since V to be admixed with theaforementioned alloy has an atomic weight approximately similar to thatof Ti or cr, it may be admixed at an elevated quantity without reducingits hydrogen storage capacity per unit weight of the alloy product somuch, but because it is very expensive, especially a highly purematerial (99.99% purity) employed for such an alloy is extremelyexpensive, the price of the alloy product results in a very high level,whereby alloy costs will increase for absorbing and storing an equalamount of hydrogen.

Therefore, for inexpensive alloys free of using precious V, Mo—Ti—Cr andW—Ti—Cr alloys are proposed wherein Mo or W is admixed as, like V, anelement highly capable of forming BCC with both Ti and Cr. However, forthese Mo and W, as suggested in Japanese Unexamined Patent Publication(Kokai) No. 10-121180 (JP, A, 10-121180), it has been reported asfollows: BCC is neither formed in such alloys even by application ofheat-treatments when at 0 at % of Mo and/or W nor obtainable as the mainphase when admixed at a low level thereof whereby no good hydrogenabsorption and desorption characteristics will appear. Accordingly,there are also problems: when the amounts of Mo and W to be admixedincrease, the hydrogen absorbing capacity per unit weight of such alloyswill lower because of their large atomic weight, and in case where thesehydrogen storage metal alloys are used as energy sources forautomobiles, bicycles, etc. in the form of hydrogen gas storage tanksand nickel hydrogen batteries, including fuel batteries, when an attemptis made at attaining a necessary electric power and hydrogen-supplyingcapacity, their weights would increase.

In view of the foregoing points, the present inventors have paid muchattention to the aforementioned problems and, as a result, succeeded inthe present invention. An object of the present invention is to provide(1) a hydrogen storage metal alloy which is (i) producible in theaforementioned form having BCC main phases even if the level of preciousV or Mo and W which each lead to a decrease in hydrogen absorbingcapacity per unit weight is made null or as minimal as possible, also(ii) excellent in view of its cost and hydrogen absorbing capacity perunit weight and (iii) highly practicable and (2) a process for producingthe same.

SUMMARY OF THE INVENTION

In order to solve the aforementioned problems, the present inventionprovides a novel hydrogen storage metal alloy for adsorption anddesorption of hydrogen. According to the present invention, the novelhydrogen storage metal alloy has the following characteristics:

-   -   (1) it has as its main phase a body-centered cubic        structure-type phase enabling the adsorption and desorption of        hydrogen, and    -   (2) it has a composition of the following general composition        formula:        Ti_((100-a-0.4b))Cr_((a-0.6b))M_(b)        wherein M is vanadium (V), provided that 20≦a (at %)≦80, and 0≦b        (at %)≦10.

Such characteristics lead to the following: the level of V can bebrought to either not more than 10 at % or 0, thereby enabling theamount of necessary precious V to be reduced or nullified, with theresult that hydrogen storage metal alloys thus obtained will becomeinexpensive, provided that other elements can be optionally admixed aslong as their admixture does not have a great influence on theaforementioned properties of the hydrogen storage metal alloys.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those wherein the atom % (at %) of element, V, containedin the metal alloy may be within a range of 6±2 at %.

As a result thereof, the alloys can have a higher hydrogen storagecapacity per unit weight within a V level range of not more than 10 at %as aforementioned.

According to the present invention, the novel hydrogen storage metalalloy also has the following characteristics:

-   -   (1) it has as its main phase a body-centered cubic        structure-type phase enabling the adsorption and desorption of        hydrogen, and    -   (2) it has a composition of the following general composition        formula:        Ti_((100-a-0.4b))Cr_((a-0.6b))M_(b)        wherein M is at least a member selected from molybdenum (Mo) and        tungsten (W), provided that 20≦a (at %)≦80, and 0≦b (at %)<5.

Such characteristics lead to the following: (1) the level of Mo or W canbe brought to either less than 5 at % or 0, thereby enabling thereduction of a hydrogen storage capacity per unit weight, depending onan increase in weight of the resultant alloy, to be minimized ornullified; and (2) since the alloys contain no precious V, they can alsobe produced inexpensively, provided that other elements can beoptionally admixed as long as their admixture does not affect greatlythe aforementioned properties of the hydrogen storage metal alloys.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those wherein the atom % (at %) of Mo and/or W, containedin the metal alloy may be within a range of 3±1.5 at %.

As a result thereof, the alloys can have a higher hydrogen storagecapacity per unit weight within a Mo and/or W level range of less than 5at % as aforementioned.

According to the present invention, the novel hydrogen storage metalalloy also has the following characteristics:

-   -   (1) it has as its main phase a body-centered cubic        structure-type phase enabling the adsorption and desorption of        hydrogen, and    -   (2) it has a composition of the following general composition        formula:        Ti_((100-a-0.4b))Cr_((a-0.6b))V_((b-c))M_(c)        wherein M is at least a member selected from molybdenum (Mo) and        tungsten (W), provided that 20≦a (at % )≦80, 0<b (at % )<10, and        0<c (at %)<5.

Such characteristics lead to the following: part of the content ofprecious V can be replaced with at least one member selected from Mo andW which are each potently capable of forming a BCC structure togetherwith Ti and Cr in the same manner as V, thereby enabling not only thecost to be relatively low but also a decrease in hydrogen storagecapacity per unit weight, brought about by the incorporation of Mo or W,to be limited to a relatively minor one, with the result that thehydrogen storage metal alloys can be produced which come to an excellentbalance between the cost and the hydrogen storage capacity per unitweight and become advantageously practicable, provided that otherelements can be optionally admixed as long as their admixture does notaffect greatly the aforementioned properties of the hydrogen storagemetal alloys.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those wherein an element, X, having an atomic radiusgreater than that of Cr but smaller than that of Ti may be contained atits atom % concentration, d (at %), ranging within 0≦d (at %)≦20.

As a result thereof, the element X can be admixed the atomic radius ofwhich is larger than that of Cr but smaller than that of Ti, therebyinhibiting the formation of a Cl4 (Laves phase) structure so as toextend a temperature range for forming a BCC structure phase in place ofthe aforementioned Cl4 (Laves phase) structure, with the result that thehydrogen storage metal alloys can be produced with the BCC structurephase in a stable fashion even at low levels of V, Mo and W, which eachhave a potent BCC structure-forming capability with both Ti and Cr.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those wherein the element, X, may include at least one ormore members selected from the group consisting of Al, Ge, Ga, Si, Auand Pt.

As a result thereof, the selected elements have an excellent capabilityof forming a metal alloy with Ti and Cr and therefore preferable to beemployed for the aforementioned element X.

It is preferred that the hydrogen storage metal alloys of the presentinvention are those wherein an element, T, may be contained at its atom% concentration, e (at %), ranging within 0≦e (at %)≦10, wherein thesaid element T includes at least one or more members selected from thegroup consisting of Nb, Ta, Mn, Fe, Al, B, C, Co, Cu, Ga, Ge, Ln (avariety of lanthanoid metals), N, Ni, P, and Si.

As a result thereof, the element T can be admixed, thereby enabling aplateau pressure at which the resultant hydrogen storage metal alloyscan absorb and release hydrogen to be appropriately controlled.

According to the present invention, a process for producing the hydrogenstorage metal alloy has the following characteristics:

for the production of hydrogen storage metal alloys having as the mainphase a body-centered cubic structure-type phase enabling the adsorptionand desorption of hydrogen, and comprising the steps of:

-   -   (1) melting a starting alloy brought to a predetermined element        ratio to form a uniform heat (melting step),    -   (2) keeping the homogenized alloy heat at a temperature within a        range just below the melting point of the alloy for a        predetermined time (heat treatment), and    -   (3) rapidly cooling the alloy after the heat treatment        (quenching step).

Such characteristics enable the production of hydrogen storage metalalloys having as the main phase a BCC-type phase with regard to not onlya Ti—Cr binary alloy, which is presumed to be hardly produced, but alsoan alloy wherein V, Mo and W are contained at low levels.

It is preferred that melting and solidification may be carried outrepeatedly predetermined times at the aforementioned melting step in thehydrogen storage metal alloy-producing process according to the presentinvention.

As a result thereof, such repeated melting and solidifying treatmentsenable us not only to produce alloys having an improved uniformitywherein a BCC-type structure phase is formed at a higher rate but alsoto prevent the occurrence of a spinodal decomposing composition as muchas possible.

It is preferred that the predetermined time range at the aforementionedheat treatment is from 1 minute to 100 hours in the hydrogen storagemetal alloy-producing process according to the present invention.

When a time range for the heat treatment step is 1 minute or less, it isimpossible to form sufficiently a BCC-type structure and when 100 hoursor more, treating costs increase due to heating for a long time. As aresult thereof, the inventive time range leads to the excellentformation of the BCC structure with minimizing an increase in thetreating cost.

It is preferred that the element ratios are those described in any ofClaims 1 to 8 regarding the aforementioned hydrogen storage metal alloyproducts obtained by the hydrogen storage metal alloy-producing processaccording to the present invention.

As a result thereof, alloys wherein the main phase is a BCC-typestructure can be produced in a stable fashion from each alloy having ahighly practicable composition according to any of Claims 1 to 8.

Described below are bases of the selected compositions for hydrogenstorage metal alloys according to the present invention. FIG. 2 depictsa Ti—Cr binary system phase diagram in connection with the presentinvention. As seen in FIG. 2, the BCC phase is present throughout allcomposition ranges of Ti and Cr over 1643K (1370° C.). In light of theatomic radius of Ti (0.147 nm) greater than that of Cr (0.130 nm), whenthe level of Ti increases and the level of Cr lessens, the alloy willincrease its BCC phase lattice constant but lower its plateau pressure.The plateau pressure of the hydrogen storage metal alloy may varydepending on its alloy-working temperature. It is preferred that theTi/Cr ratio may vary in order to acquire a desired working temperatureand consequently a suitable Ti/Cr ratio can be selected. Although astarting composition is brought to the extent of Ti₄₀Cr₆₀ in order toacquire a suitable plateau pressure at 40° C. (313K) in examples asdescribed hereinbelow, the present invention is not limited to. Theplateau pressure of such hydrogen storage metal alloys not only variesdepending on their alloy-working temperature but also is controllable byvarying a Ti/Cr ratio for Ti—Cr-M hydrogen storage metal alloysincluding Ti—Cr alloys and Ti—Cr—V alloys. The plateau pressureremarkably rises when the Cr level “a” exceeds 80 at % while the plateaupressure becomes extremely low when it is below 20 at %, thereby leadingto a poor practicability. Accordingly, it is preferred that the Ti/Crratio may be selected which is suited for a desired working temperaturewithin a range of 20≦a (at %)≦80.

Although the addition of V to such Ti—Cr binary alloys is effective infacilitating the formation of their BCC type structure asaforementioned, an excessive admixture of V leads to a decrease in theirhydrogen adsorption and desorption characteristics as shown in FIG. 5,and when the V level is over about 10 at %, the admixture of suchprecious V will not make any sense. In light of the foregoing points, itis derived that the fundamental formula:Ti_((100-a-0.4b))Cr_((a-0.6b))V_(b)will be within a range of 0≦b (at %)≦10. Further, the addition ofsubstituent element T to such alloys having the fundamental formula:Ti_((100-a-0.4b))Cr_((a-0.6b))V_(b)is effective in adjusting the plateau pressure wherein T is at least oneor more elements selected from the group consisting of Nb, Ta, Mn, Fe,Al, B, C, Co, Cu, Ga, Ge, Ln (a variety of lanthanoid metals), N, Ni, P,and Si, and an amount of substituents is 0≦c (at %)≦10.

Although Mo and W elements each have a great BCC structure-formingproperty to Ti—Cr binary alloys and the admixture of Mo or W with theTi—Cr binary alloy is effective in facilitating the formation of the BCCstructure, an excessive admixture of Mo and/or W will lead to anincrease in density for hydrogen storage metal alloy products becausesuch Mo and W are heavy elements with a relatively large atomic weight.As seen in FIGS. 9 and 10, when their level exceeds about 5 at %, thehydrogen adsorption and desorption characteristics which reach to themaximum will be led to a significant decrease. In light of the foregoingpoints, the fundamental formula:Ti_((100-a-0.4b))Cr_((a-0.4b))M_(b)wherein a is 2023 a (at %)≦80, b is 0≦b (at %)<5 and M is at least oneelement selected from Mo and W, is derived. The admixture of substituentelement T with the resultant metal alloys is also effective in adjustingthe plateau pressure in the same fashion as aforementioned, providedthat T is at least one or more elements selected from the groupconsisting of Nb, Ta, Mn, Fe, Al, B, C, Co, Cu, Ga, Ge, Ln (variouslanthanoid metals), N, Ni, P and Si, and an amount of substituents is0≦c (at %)≦10.

Further, although element V has an atomic weight approximatelyequivalent to that of Ti or Cr and is precious, even a large quantity ofits substituent leads to a less increase in molecular weight for alloyproducts whereby there is an advantage that an amount of occludedhydrogen per unit weight will not be reduced much. In contrast, since Moand W each have a great BCC structure-forming property to Ti—Cr binaryalloys, the admixture of Mo and/or W with the Ti—Cr binary alloy iseffective in facilitating the formation of BCC in alloy products.However, an excessive admixture of Mo and W will lead to a decrease inhydrogen adsorption and storage characteristics because of heavyelements each having a large atomic weight. Hence, to make better use ofboth the advantages, a novel composition is invented wherein part ofprecious V is replaced with Mo and/or W, i.e., an alloy composition ofthe following fundamental formula:Ti_((100-a-0.4b))Cr_((a-0.6b))V_((b-c))M_(c)wherein 20≦a (at %)≦80, 0≦b (at %)≦10, 0≦c (at %)<5, and M is at leastone element selected from Mo and W, is greatly practicable in view ofits cost and its occluded hydrogen quantity as well as its BCCstructure-forming capability. As before, the admixture of substituentelement T with such a composition is also effective in adjusting theplateau pressure wherein T is at least one or more elements selectedfrom the group consisting of Nb, Ta, Mn, Fe, Al, B, C, Co, Cu, Ga, Ge,Ln (various lanthanoid metals), N, Ni, P and Si.

Alloys having a low level of these elements and Mo or W are hardlyformed in the structure of BCC as pointed out in the prior art. Asapparent from the phase diagram of a Ti—Cr binary alloy (FIG. 2), thisis attributable to the fact that a temperature range for affording theBCC structure is too narrow throughout the Ti—Cr admixture ratioswherein temperature and pressure ranges at which the hydrogen storagemetal alloy can work will be within practicable values, i.e., at the Crlevel of 20 to 80 at %.

As seen in the aforementioned phase diagram (FIG. 2), however, when thelevel of Cr is gradually reduced from 60 at % (it has the same meaningas the level of Ti gradually increase from 40 at %), a temperature rangeeligible for giving a BCC structure would expand. This is presumablyattributed to the following: since the Laves phase is represented by acomposition of a AB₂ type and the atomic radius ratio of A to B(rA:rB)=about 1.225:1 is necessary for forming an ideal geometricstructure in such a composition while the atomic radius ratio of Ti toCr, both of which are used according to the present invention, is1.13:1, which is far different from the above ideal value and unsuitablefor forming the ideal Laves phase structure, Ti will quantitativelyincrease, and invade B sites in apparently more quantities wherebyconsequently the atomic radius ratio at A sites will become close tothat at B sites, thereby inhibiting the formation of Laves phases.

Now, by developing such ideas, when an element having an atomic radiussmaller than that of the A site but larger than that of the B site isadmixed therewith for substitution, not only the penetration of thesubstituent element into the A site can inhibit the formation of Lavesphase but also that into B site can it similarly.

Hence, it has been thought that there is a possibility of enabling a BCCformation in alloy products similarly to the above V case as well as theMo or W case and therefore element X (its atomic radius is smaller thanthat at the A site (Ti) but larger than that at the B site (Cr)) can beadmixed with the alloy to expand a temperature range eligible forforming BCC whereby a hydrogen storage metal alloy may be produced witha BCC structure in a more stable fashion.

The element X, the atomic radius of which is smaller than that at the Asite (Ti) but larger than that at the B site (Cr), includes, forexample, at least one or more elements selected from the groupconsisting of Al (0.143 nm), Si (0.132 nm), Ga (0.141 nm), Ge (0.137nm), Au (0.146 nm) and Pt (0.139 nm) in view of Ti atomic radius with0.147 nm and Cr with 0.130 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a process for producing the hydrogenstorage metal alloy according to an embodiment of the present invention.

FIG. 2 depicts a Ti—Cr binary system phase diagram.

FIG. 3 is an X-ray diffraction pattern of as heat-treated (at 1400° C.for 1 hour) alloyV_(x)Ti_(37.5)Cr_(62.5-x).

FIG. 4 is a graph showing hydrogen absorption and desorptioncharacteristics (at 40° C.) for as heat-treated (at 1400° C. for 1 hour)alloyV_(x)Ti_(37.5)Cr_(62.5-x).

FIG. 5 is a graph showing the relationship of admixed amounts of Vversus hydrogen absorption and desorption characteristics for a Ti—Cr—Valloy.

FIG. 6 is an X-ray diffraction pattern of as heat-treated (at 1400° C.for 1 hour) alloyTi₄₀Cr_(57.5)M_(2.5)(M=Mo, W).

FIG. 7 is a graph showing hydrogen absorption and desorptioncharacteristics (at 40° C.) for as heat-treated (at 1400° C. for 1 hour)alloy Ti₄₀Cr_(57.5)Mo_(2.5).

FIG. 8 is a graph showing hydrogen absorption and desorptioncharacteristics (at 40° C.) for as heat-treated (at 1400° C. for 1 hour)alloy Ti₄₀Cr_(57.5)W_(2.5).

FIG. 9 is a graph showing the relationship of admixed amounts of Moversus hydrogen absorption and desorption characteristics for a Ti—Cr—Moalloy.

FIG. 10 is a graph showing the relationship of admixed amounts of Wversus hydrogen absorption and desorption characteristics for a Ti—Cr—Walloy.

FIG. 11 is an X-ray diffraction pattern each of as heat-treated (at1400° C. for 1 hour) alloys Ti_(3.75)Cr₆₀V_(2.5) andTi_(37.5)Cr₆₀Mo_(1.25)V_(1.25).

FIG. 12 is an X-ray diffraction pattern each of as prepared by meltingand as heat-treated alloys Ti₄₀Cr₆₀.

FIG. 13 is an X-ray diffraction pattern each of as heat-treated (at1400° C. for 1 hour) alloy Ti_(42.5)Cr_(57.5) and as heat-treated (at1400° C. for 2 hours) alloy Ti₄₀Cr₆₀.

FIG. 14 is a graph showing hydrogen absorption and desorptioncharacteristics (at 40° C.) for as heat-treated alloyTi_(42.5)Cr_(57.5).

FIG. 15 is an X-ray diffraction pattern of as heat-treated (at 1400° C.for 1 hour) alloy Ti₄₀Cr_(57.5)Al_(2.5).

FIG. 16 is a graph of hydrogen absorption and desorption characteristics(release curve, 40° C., 5th cycle) upon application of differentialtemperature method to alloyV_(x)Ti_(37.5)Cr_(62.5-x).

BEST MODE FOR CARRYING OUT THE INVENTION

Described below are the hydrogen storage metal alloys of the presentinvention and processes of the production of the said metal alloys indetail, relying on experiments conducted by the present inventors.

First, FIG. 1 is a flow chart showing a preferred embodiment of theprocess for producing the hydrogen storage metal alloys according to thepresent invention. Such a process has been applied to the production ofhydrogen storage metal alloys used in the experiments conducted by thepresent inventors as described hereinbelow.

In this process of the production of hydrogen storage metal alloys, eachconstituent element for a desired hydrogen storage metal alloy (forexample, each of Ti, Cr and V in case of producingTi_(3.7.5)Cr₆₀V_(2.5)) was weighed at an amount corresponding to eachcomposition ratio so as to bring the total weight of a resultant ingotto 12.5 g.

Each individual metal thus weighed was thrown into an arc melting plant(not depicted), subjected to repeated treatments (melting-stirringsolidification) predetermined times (which may vary depending on thenumber of constituent elements in experiments but be usuallyapproximately 4 to 5 times) in an argon atmosphere of about 40 kPa withscrupulous care to elevate a uniformity and the resultant homogenizedingot was then maintained at a temperature region just lower than themelting point of its melt for a predetermined time to accomplish theheat treatment.

Since a temperature region at which BCC forms are produced is present atan area just below the melting temperature owned by an alloy having atarget composition as shown in the above FIG. 2 (phase diagram), theheat-treatment may be preferably effected at such a temperature regionat which the BCC is produced and just below the melting temperature. Forexample, in case of a composition containing about 60 at % of theaforementioned element Cr, although the heat-treatment is preferablyeffected by holding the molten alloy at about 1400° C., it is preferableto select a suitable heat-treating temperature from temperature areas atwhich a target alloy is produced in the form of BCC and just below themelting temperature of the target alloy, depending on its alloycomposition. Among temperature areas at which the BCC is produced andjust below the melting temperature thereof, it should be noted that itwill take a longer time to accomplish the heat-treatment when thetreatment temperature is too low (not more than about 1000° C.) while itwill take only a short time but heating will cost us too much when it istoo high. Therefore, by taking the foregoing points into account, it ispreferable to select a heat-treating temperature.

When a heat-treating time is too short, it will be impossible toaccomplish the formation of sufficient BCC structure phases while whenit is too long treating, costs will rise dependently on heating for along period. Although it is therefore preferred that the heat treatmentcan be conducted for a period suitably selected on the basis of aselected heat-treating temperature, it may be carried out preferably fora period of from 1 min to 100 hours, more preferably from 10 min to 24hours, in the embodiment, from 1 to 2 hours.

In the Examples, alloys per se were subjected to the aforementioned heattreatment after melting ingots without making any shapes. Since such aprocess does not require that cooled alloys are re-heated but enables usto produce efficiently alloy products having a BCC structure phase, itis preferable but the present invention is not limited to. For example,it may be preferred that molten alloys are shaped once by methods suchas strip casting, mono roll casting and atomizing methods to affordplates, ribbons or powders, then cooled and the resultant alloys eachhaving either the BCC phase+the Laves phase or the Laves phase alone aresubjected to the aforementioned heat treatment so as to form the BCCstructure phase as the main phase.

Among these alloys, alloys (ingots) heat treated to an extent that theBCC structure phase takes place as the main phase are rapidly cooled bydipping into ice water to give alloy products in the form of holding theabove BCC structure phase.

Although the aforementioned rapid cooling has been carried out bydipping into ice water, the present invention is not limited to and anycan be arbitrarily selected for these cooling methods. However, sincethe volume ratio of BCC structural phase varies depending on coolingrates and a slow cooling rate leads to a decrease in BCC structuralphase volume ratio, it is desired that the alloy is rapidly cooledpreferably at a cooling rate of more than 100 K/sec.

Although the alloys of the present invention have a composition apt toinduce a spinodal decomposition readily, it is defined that they areacceptable to the extent there is an unavoidable formation becausespinodal decomposing tissues cause deterioration of alloy's hydrogenabsorption and desorption characteristics.

Hereinbelow not only it has been examined and ascertained whether or notthe BCC structural phase is produced as the main phase by theaforementioned production processes for each composition but alsoexperimental results are shown which support bases of the above selectedcompositions.

An X-ray diffraction pattern of an alloy product obtained byheat-treating V_(x)Ti_(37.5)Cr_(62.5-x) alloy at 1400° C. for 1 hour isshown in FIG. 3. As apparent from FIG. 3, even when V which is presumedto be hardly utilizable in the prior art as aforementioned is admixed at2.5 at %, the BCC takes place as the main phase and when V is set to 5at % and 7.5 at %, respectively, the alloys are produced in the form ofa BCC mono phase.

The fact that each alloy as shown in FIG. 3 has the BCC structurereflects on its hydrogen absorption and desorption characteristics asshown in FIG. 4. Thus, it has been found that the BCC mono phase alloyswherein V is contained at 5 at % and 7.5 at % can absorb and releasehydrogen at about 2.8 wt % which is approximately equal to or more thanthe amount achieved by the prior art alloy containing 10 at % or more ofV. Further, it has been found that even the alloy wherein V is containedat 2.5 at % can absorb and release hydrogen at about 2.6 wt % which isapproximately equal to the amount achieved by the prior art alloycontaining 10 at % or more of V.

This is that the admixture of V with the Ti—Cr binary alloy derives anincrease in BCC structural phase volume ratio, whereby an amount ofoccluded hydrogen increases over that attained by the Ti—Cr binaryalloy. Thus, it has been found that V is an element greatly apt toproduce a BCC form and effective for bringing advantageous hydrogenabsorption and desorption characteristics owned by the BCC phase intothe Ti—Cr binary alloys. The hydrogen absorption and desorptioncharacteristics affected by amounts of admixed V in connection withthese Ti—Cr—V alloys were examined. The results are shown in FIG. 5.

The results as shown in FIG. 5 are unexpected ones. When an amount ofthe admixed element V is brought to 10 at % or more, which wasconsidered to be preferable in the prior art, it is ascertained thattarget alloys to be produced are improved for their capability offorming the BCC phase and consequently alloy products having the BCCphase become manufacturable in a stable fashion according to an increasein amount of element V to be admixed; nevertheless, it results in theirhydrogen storage capacity per unit weight equal to or less than that ofV-free Ti—Cr binary alloys (without other materials). It is thereforeapparent that their hydrogen storage capacity per unit weight reaches toa maximum at a V admixture amount of not more than 10 at %, especially6±2 at %, contrary to conventional understanding in the prior art.Accordingly, it is found that an amount of admixed V can be set to sucha region so as to not only prevent an increase in cost for alloys due toproduction by unnecessarily admixing an excessive amount of precious Vbut also increase a hydrogen storage capacity per unit weight.

Next, the aforementioned production process has been applied to Ti—Cr—Mo(W) system hydrogen storage metal alloys which have been associated withthe aforementioned problems, for example, when Mo and W which are each aheavy element having a high capability of forming BCC against Ti—Cralloys but a large atomic weight, are admixed in large quantities, thealloy products hardly exert sufficient properties, etc. Each level of Moand W therein has been examined. The results are described hereinbelow.

An X-ray diffraction pattern each of as heat-treated alloysTi₄₀Cr_(57.5)Mo_(2.5) and Ti₄₀Cr_(7.5)W_(2.5) is shown in FIG. 6. It isfound from the X-ray diffraction pattern as shown in FIG. 6 that,although Mo is admixed at a small amount, i.e., at 2.5 at % only, theresultant alloy products are in the form of a BCC mono phase. For W, BCCphases are produced as the main phase though a few Laves phases arepresent.

Further, hydrogen adsorption and desorption Characteristics of asheat-treated alloy Ti₄₀Cr_(57.5)Mo_(2.5) are shown in FIG. 7. It hasbeen noted therefrom that an amount of hydrogen occluded thereby isderived to an extent of about 2.9 wt % close to a value of 3 wt %corresponding to the maximal capacity which is considered to beintrinsically owned by the Ti—Cr binary BCC phase.

From these results, it has been found that Mo can be admixed even at asmaller amount than V so as to produce almost the BCC mono phase. Thus,it is noted that, as compared to the foregoing Ti—Cr—V alloys, an amountof additives can be reduced whereby a good property has been achieved.

Hydrogen adsorption and desorption characteristics of as heat-treatedalloy Ti₄₀Cr_(57.5)W_(2.5) are also shown in FIG. 8. Similarly to theaforementioned Mo, the W-substituted alloys come to be in the form of aBCC mono phase and their hydrogen adsorption capacity reaches to about2.7 wt % or more. When W is admixed at an amount equal to that for Mo orV, the resultant alloy products come to decrease their maximal hydrogenadsorption capacity slightly because W has a larger atomic weight. Thehydrogen adsorption and desorption characteristics which an amount eachof additives, Mo and W, affects for such heat-treated Ti—Cr—Mo andTi—Cr—W alloys are shown in FIGS. 9 and 10, respectively. When theadditive element is Mo, it has been found that the admixture of Mo at asmall amount leads to an increase in hydrogen adsorption capacity, i.e.,the hydrogen adsorption capacity becomes maximal at about 3±1.5 at % ofthe additive Mo while the hydrogen adsorption capacity comes to begradually decreased in the 5 at % or more Mo regions which have beenpresumed to be preferable in the prior art. It has also been found thatwhen Mo is admixed at 10 at % or more, the hydrogen adsorption capacitycomes to lower less than that of heat-treated Mo-free Ti—Cr alloys. Whenthe additive element is W, it has been observed that the resultant alloyproducts have a tendency similar to that for the aforementioned Mo. Ithas thus been found that the admixture of W at a small amount leads toan increase in hydrogen adsorption capacity, i.e., the hydrogenadsorption capacity becomes maximal at about 3±1.5 at % of the additiveW while the hydrogen adsorption capacity comes to be gradually decreasedin the 5 at % or more W regions which have been presumed to bepreferable in the prior art. It has also been found that when W isadmixed at 6 at % or more, the hydrogen adsorption capacity comes tolower less than that of heat-treated W-free Ti—Cr alloys.

Hence, these elements Mo and W are preferably admixed therewith at amicro amount so as to increase occupied volume ratios of the BCC phaseoccurred in such Ti—Cr binary alloys. It is found that Mo and W, ascompared for their capability of forming BCC in Ti—Cr alloys, have eacha tendency to enable the BCC-occupied volume ratio to increase even upontheir admixture at a smaller amount than V's. It is also found thatamounts per unit weight of occluded hydrogen therein come to decreasewhen they are admixed at an excessive amount.

Although each of Mo and W is admixed alone in order to clarify theefficacy of individual admixed elements in the foregoing embodiments,the present invention is not limited to. It is preferred that one of twoelements MO and W may be admixed therewith in combination with theother. For amounts of the admixed elements in this instance, it ispreferable that a total amount of admixed elements Mo and W may be lessthan 5 at %.

As aforementioned, V has an atomic weight approximately equivalent tothat of Ti or Cr. Although V is precious, molecular weights of alloyproducts are changed (increased) little even when an amount ofsubstituents increases. Therefore, there are advantages that amounts ofoccluded hydrogen do not reduce very much. Accordingly, in order toproduce BCC mono phase alloys with a high capacity by melting a largeamount of alloys followed by rapidly cooling and, if necessary,heat-treatments, it is forecasted that V may be effectively admixedtherein in combination with at least one member selected from theaforementioned Mo, W, etc. Thus, for the aforementioned Ti—Cr—V alloyswherein a low level of V is contained, which have been conventionallypresumed to be hardly produced in a BCC phase form, efficacies areexamined and proved in case where a replacement with Mo partially takesplace.

An X-ray diffraction pattern each of as heat-treatedTi_(37.5)Cr₆₀V_(2.5) and Ti_(37.5)Cr₆₀Mo_(1.25)V_(1.25) alloys is shownin FIG. 11. Reflections by the Laves phase are observed for theheat-treated alloy Ti_(37.5)Cr₆₀V_(2.5) as shown in FIG. 11 (identicalwith the pattern for X=2.5 as shown in FIG. 3) and the hydrogenadsorption and desorption characteristics only reach to an extent of2.6%. However, it has been found that the heat-treated alloyTi_(37.5)Cr₆₀Mo_(1.25)V_(1.25) wherein part of V elements are replacedwith Mo are almost in the form of a BCC mono phase and its hydrogenadsorption and desorption characteristics are improved to be an extentof about 2.7 wt %. In this way, V can be admixed therewith incombination with Mo(also W) so as to reduce an amount of precious V tobe admixed together with a reduction in amounts of Mo (and/or W) to beadmixed, with the result that the occupied volume ratio of BCC phaseswill increase together with these admixtures, thereby leading to anincrease in hydrogen adsorption capacity. Therefore, it can be said thatthe admixture of V in combination with Mo (and/or W) is a preferabletechnique for producing inexpensive hydrogen storage metal alloys with ahigh capability of absorbing and storing hydrogen.

It has been proved that, as aforementioned, by using the aboveproduction process characterized in the heat-treatment of the presentinvention the BCC phase is produced as the main phase at an area(wherein an amount each of additives V, Mo, W, etc. is extremely slight)approximately close to the Ti—Cr binary alloy which is conventionallypresumed to produce no BCC phase in the prior art and the resultantalloys exert excellent hydrogen adsorption and desorptioncharacteristics. Accordingly, it has been found that there is apossibility of acquiring excellent hydrogen adsorption and desorptioncharacteristics with regard to Ti—Cr binary alloys, i.e., alloys free ofadditives such as V, Mo and W but formed from only Ti—Cr, wherein it hasbeen presumed in the prior art that the BCC would be hardly formed asthe main phase and accordingly no good hydrogen absorption and releasewould be achieved. Next, occurred phases and hydrogen adsorption anddesorption characteristics are examined for such Ti—Cr binary alloys.

An X-ray diffraction pattern each of as prepared by melting (as cast)and as heat-treated at 1673K (kept at 1400° C. for 1 hr followed bywater-cooling) Ti₄₀Cr₆₀ is shown in FIG. 12.

It is apparent from the X-ray diffraction patterns as shown in FIG. 12that the BCC is produced as the main phase. Next, in order to have a tryat improving on Ti—Cr binary alloys for forming the BCC mono phase,researches are conducted on alloy compositions and conditions forheat-treatments. An X-ray diffraction pattern each of Ti_(42.5)Cr_(57.5)alloy materials heat-treated at 1673K (maintained at 1400° C. for 1 hrfollowed by cooling with water) and Ti₄₁Cr₅₉ alloy materialsheat-treated at 1673K wherein a time range for heat-treatment was 2hours (maintained at 1400° C. for 2 hr followed by cooling with water)is shown in FIG. 13. It is apparent from this drawing that both alloyshave the main phase of the BCC. Especially the former is produced in theform of a BCC mono phase regardless of the same heat-treating conditionsas for the alloy as shown in FIG. 12. These results indicate that thepresent invention solves the problems (it has been reported in JP, A,10-121180, Japanese Unexamined Patent Publication (Kokai) No. 10-158755(JP, A, 10-158755), Japanese Unexamined Patent Publication (Kokai) No.11-106859 (JP, A, 11-106859) that it was difficult to produce Ti—Crbinary alloys in the form of a BCC mono phase) by adjusting the alloycompositions to most suitable ones, fitting treating time, etc.

From these experimental Ti—Cr alloy results (see: FIGS. 12 and 13), itis suggested that the Laves phase formation is inhibited easier in alloyTi_(42.5)Cr_(57.5) than in alloy Ti₄₀Cr₆₀, that is, it is preventedeasier in alloys replaced with Ti having a larger atomic radius (0.147nm) than Cr (0.130 nm). The Laves phase is represented by a compositionAB₂ wherein the atomic radius ratio between both atoms A and B, i.e.,(rA:rB) is about 1.225:1 in order to have a geometrically idealstructure and also characterized by the composition ratio, A:B, having arange. However, the ratio of Ti atomic radius :Cr atomic radius is1.13:1, which is unsuitable for forming an ideal Laves phase structurefrom an initial stage, and the Ti:Cr atom % ratio, which is a target tobe researched according to the present invention, is about 1:1.5, i.e.,a large amount of Ti apparently occupies a B site, whereupon the atomicradius ratio between the A site and the B site also reduces, etc. Theseare thought to be sources for inducing results different from thosereported in the prior art.

Relying on an expansion of these ideas, the following will be expected:when a replacement with an element having an atomic radius smaller thanthe A site but greater than the B site takes place, even the intrusionof the substituent elements into A sites will lead to the inhibition ofthe Laves phase formation and that into B sites will as well. That is,it is forecasted that there are elements facilitating the formation ofBCC. It is expected that a substitution with an element (including, forexample, Al (0.143 nm), Ga (0.141 nm), Ge (0.137 nm) and Pt (0.139 nm),etc.) having an atomic radius greater than Cr (0.130 nm) but smallerthan Ti (0.147 nm) will facilitate the formation of the BCC phase.

Thus, there has been no report that the Ti—Cr binary alloy was subjectedto the formation of a BCC mono phase or the facilitation of a BCC phaseformation. This is one of bases supporting the-novelty of the presentinvention. The hydrogen absorption and desorption characteristics of asheat-treated alloy Ti_(42.5)Cr57.5 are shown in FIG. 14. Its hydrogenstorage capacity is 2.6 wt % or more. Distinctively from Ti—Cr Lavesalloys and the like as reported in the prior art, these results evidencethat the BCC phase occurring in the Ti—Cr binary alloy has advantageoushydrogen adsorption and desorption characteristics.

In connection with the fact that BCC phases occur in ternary systemalloys such as Ti—Cr—V and Ti—Cr-M (M=Mo or W) alloys, which have beendisclosed in JP, A, 10-121180, JP, A, 10-158755 and JP, A, 11-106859,the following has been experimentally proved: Ti—Cr—V alloys andTi—Cr—Mo (W) or Ti—Cr—(V or Mo) alloys according to the presentinvention are produced in the form of a BCC mono phase or in a BCC mainphase form at an extremely micro amount of V, Mo, W, etc. to be admixed(i.e., at a range very close to the Ti—Cr binary alloy), therebyexerting excellent hydrogen adsorption and desorption characteristics.This is attributed to the fact that the BCC phase of such Ti—Cr binaryalloys exerts its excellent hydrogen adsorption and desorptioncharacteristics.

An X-ray diffraction pattern each of as heat-treated alloys Ti₄₀Cr₆₀ andTi₄₀Cr_(37.5)Al_(2.5) is shown in FIG. 15. It is apparent that a BCCmono phase is almost formed by replacing part of Cr with Al. This alloyis realized by using Ti_(42.5)Cr_(57.5) alloy rather than Ti₄₀Cr₆₀ alloyas shown for Ti—Cr alloys, i.e., by developing the concept that Cr isreplaced with Ti having a larger atomic radius than Cr to bring theatomic radius ratio of A to B (rA:rB) to such an extent that it willfacilitate the inhibition of a Laves phase formation and applying Al(0.143 nm) which has an atomic radius larger than Cr (0.130 nm) butsmaller than Ti (0.147 nm) and is capable of not only inhibiting theformation of a Laves phase but also facilitating the formation of BCCeven irrespective of which of A and B sites is replaced. Elements to beadmixed therewith are those which have an action similar to Al and mayinclude Ga, Ge, Si, Pt, Au, etc.

The reason why alloys each having such an alloy composition (suchingredients) can be readily designed is that they are based on Ti—Crbinary BCC alloys in accordance with the present invention, unlike theprior art. It is reported in Japanese Patent Application No. 11-86866(or 86866/1999) that hydrogen can efficiently be utilized viaapplications of a difference in temperature, characterized in thatbody-centered cubic structure hydrogen storage metal alloys each havinga two-stage plateau or inclined plateau are subjected to an occlusion ofhydrogen at a low temperature followed by an elevation of an alloyworking temperature for at least a period of hydrogen release process.In case where the differential temperature method is applied to theaforementioned alloyV_(x)T_(37.5)Cr_(62.5-x)its hydrogen absorption and desorption characteristics are shown in FIG.16. It is apparent that the application of the differential temperaturemethod to the alloys of the present invention will lead to a hydrogenstorage capacity of about 3.0 wt %. As compared to FIG. 4, it isobserved that the differential temperature method derives an increase inhydrogen storage capacity at about 0.2 wt %, and it is thereforeexperimentally proved that the differential temperature method iseffective for alloys attained by the present invention. Itspracticability can also be understood.

1. A hydrogen storage metal alloy which has having a main phase with abody-centered cubic structure enabling the adsorption and desorption ofhydrogen, said alloy having a composition of the following generalcomposition formula:Ti_((100-a-0.4b))Cr_((a-0.6b))M_(b) wherein M is vanadium (V), providedthat 20≦a (at %)≦80, and 0≦b (at %)≦10.
 2. The hydrogen storage metalalloy according to claim 1 wherein a level of the constituent element Vcontained in the alloy is within a range of 6±2 at %.
 3. A hydrogenstorage metal alloy having a main phase with a body-centered cubicstructure enabling the adsorption and desorption of hydrogen, said alloyhaving a composition of the following general composition formula:Ti_((100-a-0.4b))Cr_((a-0.6b))M_(b) wherein M is at least a memberselected from molybdenum (Mo) and tungsten (W), provided that 20≦a (at%)≦80 and 0≦b (at %)<5.
 4. The hydrogen storage metal alloy according toclaim 3 wherein a level each of the constituent element Mo and/or Wcontained in the alloy is within a range of 3±1.5 at %.
 5. A hydrogenstorage metal alloy having a main phase with a body-centered cubicstructure the adsorption and desorption of hydrogen, said alloy having acomposition of the following general composition formula:Ti_((100-a-0.4b))Cr_((a-0.6b))V_((b-c))M_(c) wherein M is at least amember selected from molybdenum (Mo) and tungsten (W), provided that20≦a (at %)≦80, 0≦b (at %)≦10, and 0≦c (at %)<5.
 6. The hydrogen storagemetal alloy according to claim 1 wherein the element X is admixed at itsatom % concentration, d (at %), ranging within 0≦d (at %)≦20, the atomicradius of which is larger than that of Cr but smaller than that of Ti.7. The hydrogen storage metal alloy according to claim 6 wherein theelement X is at least one or more members selected from the groupconsisting of Al, Ge, Ga, Si, Au and Pt.
 8. The hydrogen storage metalalloy according to claim 1 wherein the element T is admixed at its atom% concentration, e (at %), ranging within 0≦e (at %)≦10 and includes atleast one or more members selected from the group consisting of Nb, Ta,Mn, Fe, Al, B, C, Co, Cu, Ga, Ge, a lanthanoid metal), N, Ni, P, and Si.9-12. (canceled)
 13. The hydrogen storage metal alloy according to claim3 wherein the element X is admixed at its atom % concentration, d (at%), ranging within 0≦d (at %)≦20, the atomic radius of which is largerthan that of Cr but smaller than that of Ti.
 14. The hydrogen storagemetal alloy according to claim 13 wherein the element X is at least oneor more members selected from the group consisting of Al, Ge, Ga, Si, Auand Pt.
 15. The hydrogen storage metal alloy according to claim 3wherein the element T is admixed at its atom % concentration, e (at %),ranging within 0≦e (at %)≦10 and includes at least one or more membersselected from the group consisting of Nb, Ta, Mn, Fe, Al, B, C, Co, Cu,Ga, Ge, a lanthanoid metal), N, Ni, P, and Si.
 16. The hydrogen storagemetal alloy according to claim 5 wherein the element X is admixed at itsatom % concentration, d (at %), ranging within 0≦d (at %)≦20, the atomicradius of which is larger than that of Cr but smaller than that of Ti.17. The hydrogen storage metal alloy according to claim 16 wherein theelement X is at least one or more members selected from the groupconsisting of Al, Ge, Ga, Si, Au and Pt.
 18. The hydrogen storage metalalloy according to claim 5 wherein the element T is admixed at its atom% concentration, e (at %), ranging within 0≦e (at %)≦10 and includes atleast one or more members selected from the group consisting of Nb, Ta,Mn, Fe, Al, B, C, Co, Cu, Ga, Ge, a lanthanoid metal), N, Ni, P, and Si.19. The hydrogen storage metal alloy according to claim 1 wherein thestructure comprises a mono-phase structure.
 20. The hydrogen storagemetal alloy according to claim 3 wherein the structure comprises amono-phase structure.
 21. The hydrogen storage metal alloy according toclaim 5 wherein the structure comprises a mono-phase structure.
 22. Ahydrogen storage metal alloy having a main phase with body-centeredcubic structure enabling the adsorption and desorption of hydrogen, saidalloy having a composition of the following general composition formula:Ti_((100-a-0.4b-n1[d+e]))Cr_((a-0.6b-n2[d+e]))V_((b-n3[d+e]))X_(d)T_(e)  (I) wherein X is at least one or more other elements selected from thegroup consisting of Al, Ge, Ga, Si, Au and Pt, T is at least one or moreother elements selected from the group consisting of Nb, Ta, Mn, Fe, Al,B, C, Co, Cu, Ga, Ge, a lanthanoid metal, N, Ni, P, and Si, and 20≦a (at%)≦80; 0≦b (at %)≦10; 0≦d (at %)≦20; 0≦e (at %)≦10 and n1+n2+n3=1, orTi_((100-a-0.4b-n1[d+e]))Cr_((a-0.6b-n2[d+e]))M_((b-n3[d+e]))X_(d)T_(e)  (II) wherein M is at least a member selected from molybdenum (Mo) andtungsten (W), X is at least one or more other elements elected from thegroup consisting of Al, Ge, Ga, Si, Au and Pt, T is at least one or moreelements selected from the group consisting of Nb, Ta, Mn, Fo, Al, B, C,Co, Cu, Ga, Ge, a lanthanoid metal, N, Ni, P, and Si, and 20≦a (at%)≦80; 0≦b (at %)≦5; 0≦d (at %)≦20; 0≦e (at %)≦10 and n1+n2+n3=1, orTi_((100-a-0.4b-n1[d+e]))Cr_((a-0.6b-n2[d+e]))V_((b-n3[d+e]))M_((c-n4[d+e]))X_(d)T_(e)  (III) wherein M is at least a member selected from molybdenum (Mo) andtungsten (W), X is at least one or more other elements selected from thegroup consisting of Al, Ge, Ga, Si, Au and Pt, T is at least one or moreother elements selected from the group consisting of Nb, Ta, Mn, Fe, Al,B, C, Co, Cu, Ga, Ge, a lanthanoid metal, N, Ni, P, and Si, and 20≦a (at%)≦80; 0≦b (at %)≦10; 0≦c (at %)≦5 0≦d (at %)≦20 0≦e (at %)≦10 andn1+n2+n3+n4=1.
 23. The hydrogen storage metal alloy according to claim22 wherein the elements of the alloy correspond to the composition ofthe following general composition formula:Ti_((100-a-0.4b-n1[d+e]))Cr_((a-0.6b-n2[d+e]))V_((b-n3[d+e]))X_(d)T_(e)wherein X is at least one or more other elements selected from the groupconsisting of Al, Ge, Ga, Si, Au and Pt, T is at least one or more otherelements selected from the group consisting of Nb, Ta, Mn, Fe, Al, B, C,Co, Cu, Ga, Ge, a lanthanoid metal, N, Ni, P, and Si, and 20≦a (at%)≦80; b is within a range of 6±2 (at %); 0≦d (at %)≦20; 0≦e (at %)≦10and n1+n2+n3=1.
 24. The hydrogen storage metal alloy according to claim22, wherein the structure comprises a mono-phase structure.